Surgeon-Major Thomson had apparently forgotten his appointment to view camp bedsteads, for, a few minutes after he had left Geraldine and her brother, his taxicab set him down before a sombre-looking house in Adelphi Terrace. He passed through the open doorway, up two flights of stairs, drew a key of somewhat peculiar shape from his pocket and opened a door in front of him. He found himself in a very small hall, from which there was no egress save through yet another door, through which he passed and stepped into a large but singularly bare-looking apartment. Three great safes were ranged along one side of the wall, piles of newspapers and maps were strewn all over a long table, and a huge Ordnance map of the French and Belgian Frontiers stood upon an easel. The only occupant of the apartment was a man who was sitting before a typewriter in front of the window. He turned his head and rose at Thomson’s entrance, a rather short, keen-looking young man, his face slightly pitted with smallpox, his mouth hard and firm, his eyes deep-set and bright.

“Anything happened, Ambrose?”

“A dispatch, sir,” was the brief reply.

“From the War Office?”

“No, sir, it came direct.”

Thomson drew the thin sheet of paper from its envelope and swept a space for himself at the corner of the table. Then he unlocked one of the safes and drew out from an inner drawer a parchment book bound in brown vellum. He spread out the dispatch and read it carefully. It had been handed in at a town near the Belgian frontier about eight hours before:—

Fifty thousand camp bedsteads are urgently required for neighbourhood of La Guir. Please do your best for us, the matter is urgent. Double mattress if possible. London.

For a matter of ten minutes Thomson was busy with his pencil and the code-book. When he had finished, he studied thoughtfully the message which he had transcribed:—

Plans for attack on La Guir communicated. Attack foiled. Believe Smith in London.

“Anything important, sir?” the young man at the typewriter asked.

Thomson nodded but made no immediate reply. He first of all carefully destroyed the message which he had received, and the transcription, and watched the fragments of paper burn into ashes. Then he replaced the code-book in the safe, which he carefully locked, and strolled towards the window. He stood for several minutes looking out towards the Thames.

“The same thing has happened again at La Guir,” he said at last.

“Any clue?”

“None. They say that he is in London now.”

The two men looked at one another for a moment in grave silence. Ambrose leaned back in his chair and frowned heavily.

“Through our lines, through Boulogne, across the Channel, through Dover Station, out of Charing-Cross, through our own men and the best that Scotland Yard could do for us. In London, eh?”

Thomson’s face twitched convulsively. His teeth had come together with a little snap.

“You needn’t play at being headquarters, Ambrose,” he said hoarsely. “I know it seems like a miracle but there’s a reason for that.”

“What is it?” Ambrose asked.

“Only a few weeks after the war began,” Thomson continued thoughtfully, “two French generals, four or five colonels, and over twenty junior and non-commissioned officers were court-martialled for espionage. The French have been on the lookout for that sort of thing. We haven’t. There isn’t one of these men who are sitting in judgment upon us to-day, Ambrose, who would listen to me for a single moment if I were to take the bull by the horns and say that the traitor we seek is one of ourselves.”

“You’re right,” Ambrose murmured, “but do you believe it?”

“I do,” Thomson asserted. “It isn’t only the fact of the attacks themselves miscarrying, but it’s the knowledge on the other side of exactly how best to meet that attack. It’s the exact knowledge they have as to our dispositions, our most secret and sudden change of tactics. We’ve suffered enough, Ambrose, in this country from civil spies—the Government are to blame for that. But there are plenty of people who go blustering about, declaring that two of our Cabinet Ministers ought to be hung, who’d turn round and give you the life if you hinted for a moment that the same sort of thing in a far worse degree was going on amongst men who are wearing the King’s uniform.”

“It’s ugly,” Ambrose muttered, “damned ugly!”

“Look at me,” Major Thomson continued thoughtfully. “Every secret connected with our present and future plans practically passes through my hands, yet no one watches me. Whisper a word at the War Office that perhaps it would be as well—just for a week, say—to test a few of my reports, and they’d laugh at you with the air of superior beings listening to the chatter of a fool. Yet what is there impossible about it? I may have some secret vice—avarice, perhaps. Germany would give me the price of a kingdom for all that I could tell them. Yet because I am an English officer I am above all suspicion. It’s magnificent, Ambrose, but it’s damnably foolish.”

The young man watched his chief for several moments. Thomson was standing before the window, the cold spring light falling full upon his face, with its nervous lines and strongly-cut, immobile features. He felt a curious indisposition to speak, a queer sort of desire to wait on the chance of hearing more.

“A single kink in my brain,” Thomson continued, “a secret weakness, perhaps even a dash of lunacy, and I might be quite reasonably the master-spy of the world. I was in Berlin six weeks ago, Ambrose. There wasn’t a soul who ever knew it. I made no report, on purpose.”

“Perhaps they knew and said nothing,” Ambrose suggested softly.

There was a moment’s silence. Thomson seemed to be considering the idea with strange intensity. Then he shook his head.

“I think not,” he decided. “When the history of this war is written, Ambrose, with flamboyant phrases and copious rhetoric, there will be unwritten chapters, more dramatic, having really more direct effect upon the final issue than even the great battles which have seemed the dominant factors. Sit tight here, Ambrose, and wait. I may be going over to Boulogne at any hour.”

Thomson pushed on one side the curtains which concealed an inner room, and passed through. In a quarter of an hour he reappeared, dressed in uniform. His tone, his bearing, his whole manner were changed. He walked with a springier step, he carried a little cane and he was whistling softly to himself.

“I am going to one or two places in the Tottenham Court Road, by appointment,” he announced, “to inspect some new patterns of camp bedsteads. You can tell them, if they ring up from Whitehall, that I’ll report myself later in the evening.”

Curiously enough, the other man, too had changed as though in sympathetic deference to his superior officer. He had become simply the obedient and assiduous secretary.

“Very good, sir,” he said smoothly. “I’ll do my best to finish the specifications before you return.”